Various forms of percutaneous leads have been used in both research and clinical settings for many years. For example, percutaneous synthetic arterio-venous shunts are routinely used in chronic hemodialysis, and percutaneous electrical wires have been used for neurological stimulation (e.g. artificial eye). In most cases an equilibrium state of low grade inflammation results which appears to be tolerated rather well for extended periods of time. The degree of inflammation and the extent to which it is tolerated is related to a number of factors which have, as yet, not been clearly delineated. Certainly the composition of the material, its surface texture, surface chemistry, modulus of elasticity, externally applied forces, mechanical properties, tissue reactivity, size and configuration, site of entry, and method of anchoring are all important.
Heretofore two general approaches have been taken with respect to tissue coaction with cannulae/catheters. At one extreme is the use of velour covered cannulae which elicit aggressive tissue ingrowth. Since tissue growth is roughly at a rate of 1 mm per month, the cannula is extruded outwardly as basal skin cells mature and migrate to the surface. Tissue adherence with a fixed position catheter of this type would cause discomfort to a person due to the tearing of the adhering tissue from the catheter as the tissue grows outwardly. At the other extreme the cannulae are covered with, or made of, inert, nonreactive materials such as silicone rubber or pyrolytic carbon. These inert materials eventually become completely enclosed with an epithelial pocket, resulting in a sinus tract through which bacteria can gain access to underlying tissues. Thus, heretofore good tissue bonding with movement and eventual failure by outgrowth with the living skin at the one extreme or a site of probable infection at the other extreme have been the choices available in the prior art cannulae/catheters intended for long-term emplacement.